1. Technical Field
The present disclosure relates to a method for modifying carbon nanotubes. More particularly, the present disclosure relates to a thiolation method for modifying carbon nanotubes.
2. Description of Related Art
Carbon nanotubes (CNTs) have been widely applied in numerous scientific and technological fields since being discovered. The CNTs exhibit excellent physical, thermal, and electrical properties, and thus can be applied to manufacture one-dimensional nanomaterials, novel electronic elements and devices, such as carbon nanotube field effect transistor (CNTFET) and carbon nanotube computer. The CNTs can also be applied to manufacture support materials for fuel cells or heterogeneous catalysts.
Thiol groups (—SH) exhibit excellent affinity with gold, and have been applied to self-assembly and conjugation. If the CNTs can be modified with the thiol groups, the application thereof can be broadened.
The surfaces of the CNTs can be modified with thiol groups by methods as follows. In a first method, phospholipid molecules are conjugated on the surfaces of the CNTs by noncovalent adsorption. The CNTs can be conjugated with DNA via the phospholipid molecules. However, the bonding strength of the noncovalent adsorption is weak, and thus a second method based on covalent bond is developed. In the second method, the surfaces of the CNTs are typically oxidized by an acidic mixture (sulfuric acid and nitric acid) so as to generate carboxyl groups on the surfaces of the CNTs. The carboxyl groups can be conjugated with a thiol group-containing linker through an amide bond. However, in the first and the second methods, the thiol groups are conjugated on the surfaces of the CNTs via space linkers. In other words, the thiol groups cannot be directly conjugated on the surfaces of the CNTs. When the thiolated CNTs are applied to conjugate with gold nanoparticles, a resistance between the thiolated CNTs and the gold nanoparticles may be excessive.
A third method for directly modifying the surfaces of the CNTs is developed, in which a mixture of single-wall CNTs and sulfur is treated with plasma. However, a specific equipment is required for the third method, and the specific equipment is expensive. Accordingly, it is unfavorable to apply the third method to mass production and the production cost thereof remains high.
Therefore, how to directly modify the surfaces of the CNTs with thiol groups, which is favorable to apply to mass production and has low production cost, has become an important goal of relevant academia and industry.